The number of phones capable of storing and playing music are on the rise, according to Seattle-based M:Metrics, a mobile research firm.

The United Kingdom boasts the highest penetration of these devices at 40 percent, followed by Germany (34 percent), Italy (32 percent), Spain (29 percent) and France (23 percent).

The rate in the U.S. is lower, with only 17 percent of phones, or about 33 million, capable of playing music. However, the U.S. numbers are growing quickly, with a 385 percent increase from 2006 to 2007.

Although ownership is rising, using the phone as a music player is a different matter. The percentage of users who sideloaded music -- by transferring files from a computer to a mobile device -- was only 2.9 percent in the U.S.

Still, M:Metrics expects the phone to become a common substitute for standalone music devices, such as an iPod. M:Metrics said 31 percent of those who use both a music phone and a music player in the U.S. selected their phone as their primary music device, while 11 percent use both equally.